Melting of the Mott insulating state in the lightly doped iridate (Sr_1-xLa_x)₂IrO₄

High temperature superconductivity as it manifests in the cuprates was for long time suspected to be strongly related to the copper oxide layers, and therefore specific to only this family of materials. Using spectroscopic-imaging scanning tunneling microscopy, we visualize the electronic states of the iridate (Sr_1-xLa_x)₂IrO_4, which is chemically radically different from the cuprates but also an effective Mott insulator. Above a certain doping threshold, we observe the emergence of a phase separated state, with the nucleation of pseudogap puddles and local charge order around clusters of dopant atoms [1]. At lower doping, we measure fully gapped Mott spectra, with a gap value that is in disagreement with photoemission and optical experiments. We find that this is evidence for poor electronic screening in the lightly doped iridates, and we develop an algorithm able to extract the intrinsic value of the gap, reconciling our measurement with literature and illustrating the importance of considering field penetration when performing STM experiments on poorly screened quantum materials [2].
[1] Battisti et al., Nat. Phys. 13, 21-25 (2017) [2] Battisti et al., PRB 95, 235141 (2017).